The invention relates to a fine-screened grid having a screening grate and having a motor-driven slider, which can be moved along the interior surface area of the screening grate, for clearing the screening grate. The slider may be connected with a slider arm which is disposed on a swivellable guide lever, rotatably around a pivot with its end facing away from the slider. In one position of the guide lever, the clearing position, the pivot is in a position in which the slider rests against the screening grate. In free positions, the pivot occupies a position in which the slider is away from the screening grate.
Fine-screened grids, among other uses, are used in the purification of industrial and domestic waste water. Before the waste water passes through further purification stages, coarse impurities have to be removed from it. Such a purification stage is conducted, for example, in a grit chamber in which fine-grained particles and suspended matter are removed from the waste water. However, coarse particles can also be removed from other liquids in such systems.
In the case of a fine-screened grid, the water to be purified is guided through a screening grate disposed diagonally in a water passage. The exemplary screening grate holds back fine to coarse particles corresponding to its gap width, and preferably has a curved surface. The material collecting in front of or on the screening grate is moved by means of a slider to the one end, the upper end of the screening grate, where it falls over the discharge edge of the screening grate into a container or into a conveying element. The slider moves along on a path displaced away from the screening grate to return to the start of its motion, at the lower end of the screening grate, where it resumes the purification work. Such systems are typically called fine-screened grids, operating without any limitation with respect to the size of the held-back particles.
A fine-screened grid is described in German Published Patent Application DE 41 19 593 A1. The slider is situated on a slider arm which, rotatably about a pivot with its end facing away from the slider, is disposed on a swivellable guide lever in the form of a platform. In the normal position of the guide lever, the motor-driven pivot is situated in the cylinder axis of the quarter-cylindrically constructed screening grate, so that the path of the movement of the slider during clearing of the screening grate extends directly adjacent thereto. The platform is tilted toward the rear, so that the slider can be moved on an oppositely extending path back to the start of the screening grate. The pivot is thus removed from the screening grate and the slider arrives at a certain distance marked x in the published patent application to the screening grate.
Problems occurs when using conventional fine-screened grids, such as the fine-screened grids according to the above-mentioned published patent document, because not only relatively small particles collect at the screening grate, which can be removed by the slider without any problem, but frequently also very large particles which are not typical of waste water. For example, rocks may have detached from the walls of the sewage system, or construction waste may have entered the sewage system during construction work at open sewage system intake points.
Such large particles block the slider in its clearing movement, which may eventually result in damage to the system and which will result in an interruption of the clearing operation which has to be restored immediately.
However, since such systems frequently run without monitoring, a blocking of the slider often results in a fairly long interruption before the damage can be detected and eliminated.
It is therefore an object of the invention to provide a fine-screened grid which continues to operate even when heavy and unwieldy particles are carried by the fluid being screened.
The embodiments of the invention provide a swivellable guide lever that is freely movable, so that it can be moved into the clearing position as a result of gravity on its mass, and can be moved into a free position as a result of a force applied to the slider by the material to be cleared.
In contrast to the system according to German Patent Document DE 41 19 593 A1, the guide lever of the invention is not adjustable by a motor, but can follow a movement forced onto the slider. Normally, the slider is pressed against the screening grate by the weight of the guide lever so that it is virtually moved without any gap along the screening grate. In the process, the slider takes along small particles which have not fallen through the screening grate. If larger particles are situated in front of the screening grate, the slider moves over them, in which case it moves away from the screening grate and thereby brings the guide lever into a free position. Because it is swivellable, the guide lever does not permit a return of the slider along a path at a distance with respect to the screening grate, but it enables the slider to be displaced away from the screening grate during the clearing movement in order the pass over the larger particles situated there.
In some cases, the particles are caught by the slider, so that they are taken along and cleared although the slider does not rest directly on the screening grate. However, as a rule, these large particles remain at the start of the screening grate and can be removed by other means when the opportunity arises. In this condition, the clearing performance of the fine-screened grid is limited only insignificantly. An unmonitored continuous operation is therefore possible.
The free mobility of the pivot also has the advantage that wear of the slider edge by the advancing of the pivot onto the screening grate in the clearing position is automatically compensated, so that the slider always rests closely against the screening grate, independently of the amount of wear.
The screening grate of the fine-screened grid preferably has a curved surface, particularly a quarter-cylindrical shape as illustrated in the above-mentioned published patent application. However, the bent-lever arrangement consisting of the slider arm and the guide lever, corresponding to the kinematics of such a knee shaped lever, permits the cleaning of other shapes of the curved surface of the screening grate, which may possibly be better suited to improve the clearing performance. For example, the screening grate could extend to be slightly flatter at the start end, and which becomes steeper only later, towards another end. The preferred quarter-cylinder arrangement described above is only one possible shape.
In one embodiment, a motor for the rotating drive of the slider is mounted on the pivot, and is supported by means of a torque bracket disposed on the guide lever. This configuration also increases the weight of the guide lever which presses the slider into the clearing position, which improves the clearing performance.
In another embodiment, it is practical to arrange the swivel pin of the guide lever above the screening grate with in a vertical extension of the screening grate's upper end. This configuration results in a particularly compact construction, while the guide lever is relatively long. This, in turn, has the advantage that the swiveling angle of the guide lever does not become too large even at a relatively large offset of the slider.
In one embodiment, the tilt of the guide lever with respect to a horizontal line preferably amounts to between about 30° and about 60°.
The construction of the exemplary fine-screened grid is characterized in that the screening grate may be arranged between two parallel side walls, and the guide lever is a double lever whose two lever arms are arranged outside the side walls. A curved oblong hole is formed in each side wall, with the pivot of the two lever arms extending through this oblong hole.
The arrangement has the advantage that the two lever arms are situated outside the housing formed by the two side walls and are therefore easily accessible for repair purposes. This applies particularly if, as mentioned above, the motor is fastened to one of the lever arms and thereby also remains accessible. In addition, the motor is not exposed to moisture and fogginess which forms inside the housing above the screening grate.
The clearing performance of the present device can be increased when the pivot is provided with at least two sliders and is fastened to the opposite pivot. Three sliders may also be used which may each be situated at intervals of 120° respectively. Four or more sliders may not be as practical, two sliders at a time would engage the screening grate, and would both move away from the screening grate if either one were to be displaced from the screening grate by an obstacle.
Because the fine-screened grid has one or more sliders, a continuous operation is possible, since the pivot retains its rotating direction which significantly simplifies the control of the fine-screened grid. In particular, no additional servomotor has to be provided in order to maintain a desired distance of the slider with respect to the screening grate for the return movement. In order to maintain this distance, other fine-screened grids have specialized return cranks which can be eliminated according to the present invention.
For receiving the screened material, a collecting groove with a screw conveyor or the like is connected to the upper end of the screening grate, on the other side of the discharge edge.
To improve the transfer of the screened material from the slider into the collecting groove, a rinsing system is provided which includes several rinsing nozzles aligned diagonally with respect to the area in front of the upper screening grate end. When the slider is in this upper position, the rinsing nozzles flush the screened material into the collecting groove. To prevent the flushed-in water from not running over at the exterior side of the collecting groove, the groove edge adjoining the screening grate is situated lower than the groove edge situated on the outside. This configuration ensures that excess water runs back only to the screening grate. Solid components carried along with it are thereby returned onto the screening grate.
The rinsing nozzles are preferably fastened on the housing walls and are situated above the screening grate on both sides of the vertical plane in which the slider arm is moving. The rinsing nozzles thus do not hinder the rotating movement of the slider arm and, since they are stationarily mounted, can easily be supplied with water.
To obtain a sufficiently long rinsing time, a switch is provided by means of which the position of the slider at the upper screening grate end can be determined. A control device is provided which, for a certain time period after the actuation of the switch, turns off the driving motor and turns on the rinsing system.
The invention will be explained in further detail in the following paragraphs which describe an exemplary embodiment according to the invention.